ast486: I'm supposed to go find this guy, get the plates and go back.

Unfortunately, the guys how is locked below and the door on the top of his house doesn't work at all!
Not locked, just non intractable and not destructible.

Any way to fix this or find the key?

TBreaker20: Strange, you should be able to get inside and find two thugs in there. You don't need any key to get in.

RudyLis: Waypoint glitching often, so read description, it usually gives more adequate information.
TBreaker20 is right, you don't need to search his house.